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Thursday, 10 March 2011

Discovery sheds new light on the process of stem cell generation, and will help promote safer stem-cell based studies and future clinical trialsThursday, 10 March 2011

Dr. Andras Nagy's laboratory at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital and Dr. Timo Otonkoski's laboratory at Biomedicum Stem Cell Center, University of Helsinki, as well as collaborators in Europe and Canada have identified genetic abnormalities associated with reprogramming adult cells to induced pluripotent stem (iPS) cells. The findings give researchers new insights into the reprogramming process, and will help make future applications of stem cell creation and subsequent use safer.

The study was published in Nature.

The team showed that the reprogramming process for generating iPS cells (i.e., cells that can then be 'coaxed' to become a variety of cell types for use in regenerative medicine) is associated with inherent DNA damage.

This damage is detected in the form of genetic rearrangements and 'copy number variations,' which are alterations of DNA in which a region of the genome is either deleted or amplified on certain chromosomes. The variability may either be inherited, or caused by de novo mutation.

"Our analysis shows that these genetic changes are a result of the reprogramming process itself, which raises the concern that the resultant cell lines are mutant or defective," said Dr. Nagy, a Senior Investigator at the Lunenfeld.

"These mutations could alter the properties of the stem cells, affecting their applications in studying degenerative conditions and screening for drugs to treat diseases. In the longer term, this discovery has important implications in the use of these cells for replacement therapies in regenerative medicine."

"Our study also highlights the need for rigorous characterization of generated iPS lines, especially since several groups are currently trying to enhance reprogramming efficiency," said Dr. Samer Hussein, a McEwen post-doctoral scientist who initiated these studies with Dr. Otonkoski, before completing them with Dr. Nagy.

"For example, increasing the efficiency of reprogramming may actually reduce the quality of the cells in the long run, if genomic integrity is not accurately assessed."

The researchers used a molecular technique called single nucleotide polymorphism (SNP) analysis to study stem cell lines, and specifically to compare the number of copy number variations in both early and intermediate-stage human iPS cells with their respective parental, originating cells.

Drs. Nagy and Otonkoski and their teams found that iPS cells had more genetic abnormalities than their originating cells and embryonic stem cells. Interestingly, however, the simple process of growing the freshly generated iPS cells for a few weeks selected against the highly mutant cell lines, and thus most of the genetic abnormalities were eventually 'weeded out.'

"However, some of the mutations are beneficial for the cells and they may survive during continued growth," said Dr. Otonkoski, Director and Senior Scientist at the Biomedicum Stem Cell Center.

Stem cells have been widely touted as a source of great hope for use in regenerative medicine, as well as in the development of new drugs to prevent and treat illnesses including Parkinson's disease, spinal cord injury and macular degeneration. But techniques for generating these uniquely malleable cells have also opened a Pandora's Box of concerns and ethical quandaries. Health Canada, the U.S. Food and Drug Administration and the European Union consider stem cells to be drugs under federal legislation, and as such, subject to the same regulations.

"Our results suggest that whole genome analysis should be included as part of quality control of iPS cell lines to ensure that these cells are genetically normal after the reprogramming process, and then use them for disease studies and/or clinical applications," said Dr. Nagy.

"Rapid development of the technologies in genome-wide analyses will make this more feasible in the future," said Dr. Otonkoski.

"In addition, there is a need to further explore if other methods might mitigate the amount of DNA damage generated during the generation of stem cells," both investigators agreed.

About the Samuel Lunenfeld Research Institute of Mount Sinai HospitalThe Samuel Lunenfeld Research Institute of Mount Sinai Hospital, a University of Toronto affiliated research centre established in 1985, is one of the world's premier centres in biomedical research. Thirty-six principal investigators lead research in diabetes, cancer biology, epidemiology, stem cell research, women's and infants' health, neurobiology and systems biology.

About Biomedicum HelsinkiBiomedicum Helsinki, located on the Meilahti Campus of the University of Helsinki, is one of the leading medical research institutions in Scandinavian countries, hosting about 200 principal investigators of the University of Helsinki and Helsinki University Central Hospital. Research strengths of Biomedicum Helsinki encompass topics in basic and clinical science related to molecular and cellular biology, molecular genetics, cancer biology, neuroscience, endocrinology, stem cell biology, and metabolic diseases.

Scientists have discovered a new way to generate human motor nerve cells in a development that will help research into motor neurone disease Thursday, 10 March 2011

Scientists have discovered a new way to generate human motor nerve cells in a development that will help research into motor neurone disease.

A team from the Universities of Edinburgh, Cambridge and Cardiff has created a range of motor neurons – nerves cells that send messages from the brain and spine to other parts of the body – from human embryonic stem cells in the laboratory.

It is the first time that researchers have been able to generate a variety of human motor neurons, which differ in their make-up and display properties depending on where they are located in the spinal cord.

The research, published in the journal Nature Communications, could help scientists better understand motor neurone disease. The process will enable scientists to create different types of motor neurons and study why some are more vulnerable to disease than others.

Motor neurons control muscle activity such as speaking, walking, swallowing and breathing. However, in motor neurone disease – a progressive and ultimately fatal disorder – these cells break down leading to paralysis, difficulty speaking, breathing and swallowing.

Previously scientists had only been able to generate one particular kind of motor neuron, which they did by using retinoic acid, a vitamin A derivative.

In the latest study, scientists have found a way to generate a wider range of motor neurons using a new process without retinoic acid.

Professor Siddharthan Chandran, Director of the Euan MacDonald Centre for Motor Neurone Disease Research at the University of Edinburgh, said:

"Motor neurons differ in their make-up, so understanding why some are more vulnerable than others to disease is important for developing treatment for this devastating condition."

Dr Rickie Patani, of the University of Cambridge, said:

"Although motor neurons are often considered as a single group, they represent a diverse collection of neuronal subtypes. The ability to create a range of different motor neurons is a key step in understanding the basis of selective subtype vulnerability in conditions such as motor neuron disease and spinal muscular atrophy."

An international study shows that reprogramming cells leads to genomic aberrationsThursday, 10 March 2011

It's a discordant note in the symphony of good news that usually accompanies stem cell research announcements. Stem cells hold enormous promise in regenerative medicine, thanks to their ability to regenerate diseased or damaged tissues. They have made it possible to markedly improve the effectiveness of many medical treatments – muscle regeneration in cases of dystrophy, skin grafts for treating burn victims, and the treatment of leukaemia via bone marrow transplants.

The problem is obtaining them. Those that are the true source of life, in the first days of embryonic development, are of course the most highly sought after; still undifferentiated, they are "pluripotent," meaning they can evolve into liver, muscle, eye – any kind of cell. But the issue of how to obtain them clearly raises insurmountable ethical questions.

"In this regard, the recent discovery of the "reprogramming" phenomenon, by which somatic cells can be induced to convert to a pluripotent state simply by forcing the expression of a few genes, opens a phenomenal number of possibilities in regenerative medicine," says Didier Trono, Dean of the EPFL School of Life Sciences.

"Imagine, for example, collecting a few cells from the hair follicle of a haemophiliac patient, reprogramming them to the pluripotency of their embryonic precursor, correcting the mutation responsible for the coagulation disorder that plagues the patient, and then re-administering them, genetically "cured," after having orchestrated a differentiation into fully functional progeny."

Increased risks for cancer?
But a study that has just been published in the journal Cell Death and Differentiation, to be followed by two articles in the journal Nature, is dampening those hopes. Conducted by the Department of Biochemistry at the University of Geneva and the European Institute of Oncology in Milan, with the participation of Trono's laboratory, it concludes that these reprogrammed cells exhibit a "genomic instability" that appears to be caused by the process used to return the cells to their embryonic state. Even more serious, the genetic mutations observed resemble mutations that are found in cancer cells. The scientists draw the conclusion that reprogrammed stem cells need to be extensively investigated before they can even be considered for use in regenerative medicine.

The experiments were done using mouse mammary and fibroblast cells. The researchers used three different processes for reprogramming the cells to a "stem," or embryonic, state. The first method was developed expressly for this study, and the others have already been well documented.

Yet all the processes led to the same, implacable conclusion: the genetic anomalies multiplied, in a manner that seems to indicate that they are inherent to the reprogramming process itself, which typically makes use of oncogenes.

"Interestingly, oncogenes have the potential to induce genomic instability," the authors explain.

These results underline the necessity of conducting further studies. First, to see if the genetic anomalies are serious enough to compromise the function and stability of cells regenerated using the reprogrammed cells; and second, to "refine the methods used for generating induced pluripotent cells, in order to avoid this problem. These results will thus motivate scientists to come up with a solution," concludes Trono.